1. Field of the Invention
The present invention relates generally to the wireless telecommunications field and, in particular, to the forwarding of short text messages to mobile subscribers in a cellular communications system.
2. History of Related Art
The Global System for Mobile Communications (GSM) is a digital, mobile cellular radiotelephone system that has been introduced as a standard in several European countries. The basic telecommunications services supported by the GSM include two-way voice communications between fixed and mobile subscribers, CCITT Group 3 facsimile transmissions, and synchronous and asynchronous data transmissions at rates of up to 9.6 kbits/s.
A special telecommunications service supported by the GSM is the Short Message Service (SMS). The SMS enables the GSM to route short text messages, each up to 160 alphanumeric characters long, over the signaling channels to or from mobile stations. If a mobile station for which a short message is intended is not in service, or has left the coverage area, the message is stored in a Short Message Service Center (SMS-C). The SMS-C forwards the message to the mobile station when it returns to service or re-enters the coverage area. The SMS can also transfer short messages between a Short Message Service Terminal (SMT) in a data network and GSM mobile stations.
The GSM is divided into a switching subsystem and base station subsystem. A call from a mobile station is received by a base transceiver station, which is part of the base station subsystem. The base transceiver station defines an individual cell in a geographical service area. A base station controller also in the base station subsystem controls a group of base transceiver stations (cells) . A number of base station controllers are served by a mobile services switching center (MSC), which forms a part of the switching subsystem. The MSC controls calls to and from other telephone and data communications systems, such as a Public Switched Telephone Network (PSTN), Integrated Services Digital Network (ISDN), Public Land Mobile Network (PLMN), and various public and private data networks.
If a user in another network (e.g., PSTN) calls a GSM subscriber, the call is connected to a gateway MSC (GMSC). The GMSC finds the location of the GSM subscriber by interrogating a home location register (HLR), which is a database in the switching subsystem. The HLR provides the address of the GSM subscriber in its most current MSC area. The GMSC routes the call to that MSC. The current location of the GSM subscriber is maintained in a visitor location register (VLR), a database containing information about all of the GSM subscribers currently located in that MSC's area. If the GSM subscriber roams into a new MSC area, the VLR associated with the new MSC requests information about the subscriber from the HLR. At the same time, the HLR is informed about the new MSC area in which the subscriber resides.
In the GSM, a short message can be mobile originated or mobile terminated. A mobile originated short message is submitted from a mobile terminal via a base transceiver station to the visited MSC. The visited MSC forwards the message to the SMS-C given by the originating mobile terminal. The SMS-C forwards the message to its destination, which can be a mobile station or a terminal in the data network.
A mobile terminated short message is submitted by a user directly to an SMS-C. The SMS-C forwards the message to a short message service-gateway mobile service center (SMS-GMSC). The SMS-GMSC interrogates the related HLR for transporting information, and reroutes the message to the appropriate MSC. The destination mobile station is paged and a connection is set up between the MSC and the mobile station. Upon set up, the MSC forwards the message in the SMS-C to the mobile station via the signaling channel (e.g., stand alone dedicated control channel or SDCCH). If the message was delivered successfully, a notification report is sent from the MSC to the originating SMS-C. If not, the HLR is so informed and a failure report is sent from the MSC to the originating SMS-C. The notification report or failure report can be sent to the message originator by the SMS-C.
A significant problem arises if numerous SMS-Cs are connected to the mobile network (e.g., to increase the network's SMS capacity). For example, a number of mobile subscribers can each have a personal mailbox. A personal mailbox is a (memory) location in an SMS-C that contains a subscriber's profile for handling incoming short messages, such as, for example, converting an incoming short message to an e-mail format and routing it to an e-mail inbox, or screening incoming messages from certain originating addresses. Notably, the personal mailbox concept can work properly only if all of the short messages intended for a specific subscriber pass through that subscriber's personal mailbox. In other words, all of the subscriber's incoming short messages should pass through one SMS-C containing that subscriber's personal mailbox. However, since mobile stations can roam from one service location to another, different SMS-Cs connected to the network by their respective MSCs can end up storing different short messages intended for a specific subscriber. Consequently, the conventional short message services are not compatible with the concept of a personal mailbox.
Another significant problem arises if numerous SMS-Cs are connected to a mobile network. If the mobile network provides a short message alerting function (e.g., indicating to an SMS-C that a mobile station has contacted the network and a message can be delivered), all of the SMS-Cs that are holding messages for that mobile subscriber will be alerted. Albeit, storing short messages for specific mobile subscribers at different SMS-Cs is a great waste of SMS and network capacity. More importantly, however, the different SMS-Cs' attempts to deliver their respective messages to a specific mobile station results in message collisions, since those different delivery attempts are not coordinated.